Removable disk cartridges for storing digital electronic information typically comprise an outer casing or shell that encloses a magnetic, magnetic-optical, or optical disk upon which information can be stored. The cartridge shell often comprises upper and lower halves that are joined together during the manufacturing process of the cartridge. The disk medium is mounted on a hub that rotates freely within the shell. When the cartridge is inserted into a disk drive, a spindle motor in the drive rotates the disk via a hub disposed in the center of the disk. The cartridge shell is typically equipped with an aperture which provides the read/write heads of the disk drive with access to the disk medium. A shutter or door mechanism is often provided to cover the aperture when the cartridge is not in use, thereby inhibiting dust and other contaminants from entering the cartridge and settling on the medium.
Some contaminants inevitably reach the surface of the disk medium during normal use of the cartridge, despite the presence of the cartridge shell and the shutter mechanism. Such contaminants typically originate in the ambient environment and reach the medium through various openings in the shell, e.g., the access opening for the disk hub. Furthermore, magnetic particles may be generated during the cartridge's manufacturing process, and during read/write operations within the disk drive. The noted contaminants can damage the disk medium and the heads of the disk drive, and can lead to a loss of data.
The problem of disk contamination is typically addressed by placing one or more fabric liners on an inner surface of the cartridge shells. These liners often comprise a mixture of non-woven fibers bonded together by a thermal or an adhesive process. A hydroentangling process such as that described in U.S. Pat. No. 5,311,389 may also be used to bond the fibers. An example of a fabric liner is the "DATAPROTECH" liner, manufactured by the Veratec Division of International Paper Co., Walpole, Mass. This particular liner comprises mixture of rayon (80%) and nylon (20%) fibers.
Data-cartridge liners are typically affixed to the upper and lower halves of the cartridge shell, and thus form surfaces that lie directly above and below the surface of the medium. Some type of contact is typically set between the surface of the liner and the disk medium. This contact results in a brushing or wiping motion on the medium's surface as the medium rotates, thereby removing contaminants from the surface.
One method for bringing about contact between the liner and the disk medium is through the use of lifters and opposing ribs. The lifters and ribs are positioned on the inner surface of the cartridge shells, and cooperate in a manner that forces the liner against at least a portion of the medium. This concept is illustrated in U.S. Pat. Nos. 4,750,075; 5,006,948; 5,083,231; and 5,216,566. While the use of lifters and ribs ensures that the liner contacts and wipes the surface of the medium, the force with which the liner is pressed against the medium typically creates a significant amount of drag on the medium during rotation. Higher levels of drag necessitate the use of a relatively strong disk-drive motor to rotate the medium (thereby increasing the cost and size of the disk drive). Additionally, relatively high contact pressure accelerates wear of the medium's surface.
An improved method for cleaning the surface of a data-storage medium has been developed. This methodology is based on the use of raised fibers disposed along the surface of the cartridge liner to wipe the surface of the medium (these surface fibers can be visualized as the "fluff" or "fuzz" which forms on the surface of most fibrous materials). The noted methodology is described in detail in pending U.S. patent application Ser. No. 08/613,880, entitled "Fuzzed Fabric Liner for a Disk Cartridge." The use of raised surface fibers to wipe the medium significantly reduces the contact pressure between the liner and medium, thereby alleviating the disadvantages associated with relatively high contact pressures.
The effectiveness of the above-noted methodology is dependent upon the density in which the raised fibers are distributed along the liner surface. The density of the raised surface fibers is set during the manufacturing process of the liner. Specifically, the liner is "fluffed" by brushing and vacuuming the liner surface in a controlled manner. This process causes the bonded surface fibers to loosen or break, and to extend upward from the surface, thereby forming fluff on the surface of the liner. The amount of fluff disposed along the surface is subsequently checked due to the importance of this parameter to the longevity of the disk medium. Specifically, the density in which the raised fibers are disposed along the liner surface is quantified in relation to some measurable baseline.
The noted fluff check is currently performed by measuring the torque required to rotate the disk medium within a fully-assembled cartridge. This methodology is based on the principle that the fibers in contact with the medium generate a force which opposes the medium's rotation. The magnitude of this force is proportional to the degree of contact between the fibers and the liner, which in turn is proportional the amount of liner fluff present. Hence, the amount of fluff can be determined by comparing the measured rotation torque to a previously-established baseline which relates rotation torque to liner fluff.
The rotation-torque methodology has several significant disadvantages. Specifically, the check can only be performed after the cartridge has been fully assembled. Hence, a check cannot be performed at the liner's point of manufacture if the manufacturing location differs from the cartridge-assembly location. Furthermore, identification of a defective liner will necessitate the disassembly or scrapping of a fully-assembled cartridge. Both of these factors adversely affect production efficiency and cost.
A further disadvantage of the currently-practiced fluff check arises from the fact that the results of the check can be influenced by variables in addition to liner fluff. For example, the torque required to rotate the disk medium is influenced by factors such as friction between the shell of the data-storage cartridge and the disk hub. Such additional variables skew the relationship between liner fluff and rotation torque, thereby reducing the precision of the check. Lower levels of precision in production checks generally necessitate corresponding reductions in rejection thresholds. Hence, the currently-practiced methodology can lead to the rejection of liners which, in reality, possess acceptable fluff characteristics.
Thus, a need exists for an improved system and an improved method for measuring the fluff present on fabric liners used in data-storage cartridges.